Canada Post mails me a $1.04 courtesy card

The other day my utility company mailed me an informational type letter and did not put a stamp on it.  To my surprise the letter was still delivered but Canada Post had attached a "$1.04 Postage Due" card.

"With this card you received mail that was sent without enough postage.  To avoid delay and inconvenience, the amount due was not collected at the time of delivery.  Please affix the postage on the other side of this card to cover the amount due, and mail the card.  Your postmaster".

Since when do I have to pay for mail from somebody else?  I dropped by the post office to ask them that very question and their response was "Oh this is just a courtesy card" and proceeded to throw the card out.

Oh, so the courtesy is to make me waste my time to come to the post office to pay $1.04 that I don't really have to?  How is that a courtesy?

Whatever, I was so glad that I didn't have to fight further about the $1.04 that I left without further questioning...